Sample preparation for the chromatographic determination of ecdysteroids using solid-phase extraction methods

The ecdysteroids are hormones widely distributed in insects and crustaceans, where they are involved in the regulation of moulting. Methods of sample preparation based on solid-phase extraction of the ecdysteroids from biological samples for subsequent chromatographic analysis are reviewed. Most methods use an initial partition of the sample (or extract) between water or aqueous methanol with a non-polar solvent to remove lipids. The aqueous portion is applied to a cartridge containing C₁₈-bonded silica gel. Removal of polar impurities is then effected, followed by recovery of the ecdysteroids from the cartridge and chromatographic analysis. Results are given for the use of phenylboronic acid (PBA) bonded to silica gel as a means of obtaining a much more specific method of extraction. The PBA phase was shown to have a high affinity for ecdysteroids containing a 20,22-cis-diol but not for compounds possessing only a 2,3-cis-diol.